This invention relates to an airborne power control system and method and more particularly to a power control system and method for automatically controlling power during the landing of an aircraft.
The need for a highly reliable and safe automatic landing system for aircraft has been recognized. It has also been recognized that any such system should be fully operable under adverse weather conditions with reliability. Such systems must automatically land an aircraft safely in fog or rain, at night, with heavy payloads and produce a smooth landing under any such conditions.
In order to meet the requirements for reliability and to provide for smooth landings under adverse conditions, anautomatic landing system must contain control equipment which is insensitive to outside disturbances normally encountered in landings.
In the past, various control systems have been used to control aircraft in-flight. For example, glide slope systems have been used to guide an aircraft down to a flare altitude of about 50 feet. However, at flare altitude, other means of control are provided to alter the aircraft""s flight path and achieve a touchdown at a much reduced rate of descent.
One system for automatically landing an aircraft is disclosed in the U.S. Pat. No. 3,031,662 of Bond. In that system, a flare path is provided which accurately controls the rate of descent of the aircraft in proportion to the altitude. If the rate of descent of an aircraft is controlled in proportion to altitude, an exponential flare may be obtained which provides the necessary flare path to meet the design requirements.
In the preferred embodiment of the Bond system, the altitude and altitude rate signals are obtained from a radio altimeter and the acceleration signal is obtained from a vertical accelerometer. The three signals are then combined to provide an indication to an automatic control system of the relation of the actual landing path described by the aircraft to the theoretical curve described by an altitude equation.
Notwithstanding past developments and the need for reliable automatic landing system, such systems have not enjoyed widespread commercial success. It is believed that such systems fail to provide the needed flexibility, reliability and rapid response time to accommodate rough air, head and tail wind oscillations and other weather related problems.
It is now believed that there may be a large commercial demand for an improved control system for landing an aircraft in accordance with the present invention. Such systems will provide automatic landing from flare to touchdown and control the curvilinear flight path for the final 50 feet of descent. It is believed that there is a demand for a system and method which controls two; parameters of importance, i.e. the vertical velocity and airspeed. Such systems and methods must maintain certain minimum airspeed and at the same time provide sufficient lift to prevent the aircraft from stalling.
In essence, the present invention contemplates an airborne safe landing power control system and method. The system comprises an airborne computer and means for entering a minimum airspeed program as a function of altitude in said computer. The system also includes means such a radio altimeter for sensing the instantaneous altitude of the aircraft and means for sensing the aircraft""s vertical velocity during a landing maneuver, i.e. from about 50 feet altitude to touchdown. Means for measuring airspeed are also provided. In addition, the system includes comparator means for comparing the programmed airspeed with the actual airspeed at a given altitude. Key elements of the system include throttle retard means such as a servomotor for decreasing the engine thrust when the actual airspeed exceeds the programmed airspeed at any given altitude and inhibiting means for inhibiting the throttle retard means if the airspeed drops below the programmed airspeed.